1. Field of the Invention
The present invention relates to a method and a device for determining a fuel portion (i.e., percentage or ratio) in an engine oil of a motor vehicle.
2. Prior Art
During operation of internal combustion engines of motor vehicles, fuel can enter the engine oil. This risk occurs in particular before the engine has reached its operating temperature, that is to say in the cold state. Before the operating temperature of the internal combustion engine is reached there is often incomplete combustion of the supplied fuel. The fuel can then precipitation the cylinder walls and enter the engine oil. Furthermore, in the cold state of the engine there are air gaps between engine components as a result of which the unburned fuel can enter the engine oil. Owing to their non-volatile components this problem occurs in particular with diesel fuels. In this context fuel can particularly frequently enter the engine oil in the case of what are referred to as bio-diesel fuels, that is to say diesel fuels on a plant basis, which are acquired from plant oils or animal fats since these fuels likewise do not always burn completely when the operating temperature of the internal combustion engine is reached.
The engine oil performs a multiplicity of important tasks in an internal combustion engine. The engine oil serves predominantly to lubricate the parts which move in relation to one another in internal combustion engines. Furthermore, friction heat is carried away by the engine oil, impurities are washed out, and metal parts are protected against corrosion. The fuel that enters the engine oil greatly increases the engine wear, often accompanied by an increase in the fuel consumption and the emission of pollutants by the internal combustion engine.
In order to solve this problem, in the past the engine oil changing intervals have been correspondingly shortened when bio-fuels are used. However, before the oil change it is not possible to obtain information as to whether the oil change is actually necessary at this time owing to an increased fuel portion in the engine oil. Unnecessary oil changes are therefore carried out under certain circumstances.